The encapsulation of electronic components represents an art in and of itself. Electronic components are encapsulated to maintain electrical insulation, to provide mechanical protection and to otherwise shield the component from exposure to its environment. As the evolution of electronics continues its rapid advance it becomes increasingly important that the art and technology of encapsulation keep pace. An area of significant concern and interest relates specifically to the compositions used to encapsulate electronic components. There is an on-going effort to discover new and improved encapsulation materials. The present invention represents a contribution to that effort.
A relatively recent development has been the use of poly(arylene sulfide) compositions such as, for example, poly(phenylene sulfide) compositions, as encapsulating materials. These compositions typically represent a carefully balanced blend of at least 3 ingredients: (1) poly(arylene sulfide), (2) glass fibers and (3) filler (such as silica or talc). In addition relatively small amounts of other components such as, for example, colorants, flow improvers, processing aids, organosilanes and the like, can be present.
An example of a composition especially well suited for the encapsulation of active electronic components is presented below:
______________________________________ (a) poly(phenylene sulfide) 35 wt % (b) glass fibers 15 wt % (c) silica 49 wt % (d) 3-mercaptopropyltrimethoxysilane 1 wt % ______________________________________
This composition additionally includes colorants, flow improvers and processing aids to suit the particular circumstances.
One very important property of any encapsulation material is electrical resistance. In use, the encapsulation material is generally subjected to a hostile environment that adversely affects the desired properties of the material. Of particular concern are the effects of high temperature conditions and/or of high humidity conditions. Such conditions can cause a decrease in the electrical resistance of the encapsulation material.
It is an objective of those of skill in the art of poly(arylene sulfide) encapsulation compositions to produce compositions which retain high electrical resistance when subjected to hostile conditions such as, for example, high temperature and high humidity. It is also an objective of those of skill in this art to produce poly(arylene sulfide) compositions of increased electrical resistance.
The utility of an encapsulation material is not evaluated solely on the basis of electrical resistance. Electronic components can be damaged when encapsulated with the material. The dislocation or breakage of wires is referred to as wire wash. The dislocation of parts (such as, for example, semiconductor chips) can also be a problem. It is an objective of those of skill in the art to provide encapsulation materials having a reduced tendency to cause wire wash. It is also an objective to provide encapsulation materials exhibiting improved performance in electrical yield tests and in reliability tests.